Limits...
Uneven distribution of enamel in the tooth crown of a Plains Zebra (Equus quagga).

Winkler DE, Kaiser TM - PeerJ (2015)

Bottom Line: They have to be partially worn to expose enamel ridges which can then act as shear-cutting blades to break the food down.We use the Plains Zebra (Equus quagga) as a hypsodont, herbivorous model organism to investigate how initial wear of the tooth crown is controlled by underlying structures.We find that the enamel proportion is smaller at the apical half of the tooth crown in all upper tooth positions and suggest that lower enamel content here could promote early wear.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center of Natural History (CeNak), University of Hamburg , Hamburg , Germany.

ABSTRACT
Unworn teeth of herbivorous mammals are not immediately functional. They have to be partially worn to expose enamel ridges which can then act as shear-cutting blades to break the food down. We use the Plains Zebra (Equus quagga) as a hypsodont, herbivorous model organism to investigate how initial wear of the tooth crown is controlled by underlying structures. We find that the enamel proportion is smaller at the apical half of the tooth crown in all upper tooth positions and suggest that lower enamel content here could promote early wear. Besides this uneven enamel distribution, we note that the third molar has a higher overall enamel content than any other tooth position. The M3 is thus likely to have a slightly different functional trait in mastication, resisting highest bite forces along the tooth row and maintaining functionality when anterior teeth are already worn down.

No MeSH data available.


Related in: MedlinePlus

Permanent dentition of Equus quagga.Virtual 3D-model of the permanent upper right dentition of Equus quagga, no. 70335. As typical in hypsodont species, the tooth crowns are much longer than wide. Arrows point towards apical. (A) Anatomical position. Note that the caps of the deciduous premolars have been lost, but would have been present at this life stage. (B) Occlusal view. Scale bar 1 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4465953&req=5

fig-1: Permanent dentition of Equus quagga.Virtual 3D-model of the permanent upper right dentition of Equus quagga, no. 70335. As typical in hypsodont species, the tooth crowns are much longer than wide. Arrows point towards apical. (A) Anatomical position. Note that the caps of the deciduous premolars have been lost, but would have been present at this life stage. (B) Occlusal view. Scale bar 1 cm.

Mentions: Hypsodonty has been defined as the relative increase in the height of cheek teeth (Van Valen, 1960), or more simply as larger tooth crown height compared to tooth crown length (White, 1959; Thenius, 1989; compare Fig. 1). It is a common evolutionary strategy of herbivorous mammals to counter high abrasive loads in the ingested diet, which result in a high degree of dental wear. Following White (1959), cusp hypsodonty, tooth base hypsodonty and root hypsodonty can be distinguished, depending upon which structure is elongated. Hypsodonty can be easily achieved in all tooth positions by extending specific ontogenetic phases during tooth development (von Koenigswald, 2011). Newly erupted hypsodont cheek teeth share a feature among all taxa: they are not immediately functional. To comminute tough plant matter, the relatively rounded apex of the (pre)molar tooth crowns has to wear down slightly, exposing the enamel ridges which may then act as shearing blades during mastication. The rapid wear of the topmost tooth crown has been noted in selenodont molars (Osborn & Lumsden, 1978), and several authors have hypothesised how this initial wear is facilitated. One theory is that empty chewing movements (thegosis) sharpen teeth in adults and initiate wear in young animals (Every, 1972; Teaford & Walker, 1983; Every, Tunnicliffe & Every, 1998). More often, however, such empty chewing is considered a behavioural anomaly (termed bruxism or pathological thegosis) which appears in livestock, other domestic or captive animals (e.g., Murray & Sanson, 1998; Troxler, 2007; Troxler, 2012) and also in man (Manfredini et al., 2013). We do not think that thegosis is needed to initiate functionality and a lack of empirical data are available in support of this hypothesis.


Uneven distribution of enamel in the tooth crown of a Plains Zebra (Equus quagga).

Winkler DE, Kaiser TM - PeerJ (2015)

Permanent dentition of Equus quagga.Virtual 3D-model of the permanent upper right dentition of Equus quagga, no. 70335. As typical in hypsodont species, the tooth crowns are much longer than wide. Arrows point towards apical. (A) Anatomical position. Note that the caps of the deciduous premolars have been lost, but would have been present at this life stage. (B) Occlusal view. Scale bar 1 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465953&req=5

fig-1: Permanent dentition of Equus quagga.Virtual 3D-model of the permanent upper right dentition of Equus quagga, no. 70335. As typical in hypsodont species, the tooth crowns are much longer than wide. Arrows point towards apical. (A) Anatomical position. Note that the caps of the deciduous premolars have been lost, but would have been present at this life stage. (B) Occlusal view. Scale bar 1 cm.
Mentions: Hypsodonty has been defined as the relative increase in the height of cheek teeth (Van Valen, 1960), or more simply as larger tooth crown height compared to tooth crown length (White, 1959; Thenius, 1989; compare Fig. 1). It is a common evolutionary strategy of herbivorous mammals to counter high abrasive loads in the ingested diet, which result in a high degree of dental wear. Following White (1959), cusp hypsodonty, tooth base hypsodonty and root hypsodonty can be distinguished, depending upon which structure is elongated. Hypsodonty can be easily achieved in all tooth positions by extending specific ontogenetic phases during tooth development (von Koenigswald, 2011). Newly erupted hypsodont cheek teeth share a feature among all taxa: they are not immediately functional. To comminute tough plant matter, the relatively rounded apex of the (pre)molar tooth crowns has to wear down slightly, exposing the enamel ridges which may then act as shearing blades during mastication. The rapid wear of the topmost tooth crown has been noted in selenodont molars (Osborn & Lumsden, 1978), and several authors have hypothesised how this initial wear is facilitated. One theory is that empty chewing movements (thegosis) sharpen teeth in adults and initiate wear in young animals (Every, 1972; Teaford & Walker, 1983; Every, Tunnicliffe & Every, 1998). More often, however, such empty chewing is considered a behavioural anomaly (termed bruxism or pathological thegosis) which appears in livestock, other domestic or captive animals (e.g., Murray & Sanson, 1998; Troxler, 2007; Troxler, 2012) and also in man (Manfredini et al., 2013). We do not think that thegosis is needed to initiate functionality and a lack of empirical data are available in support of this hypothesis.

Bottom Line: They have to be partially worn to expose enamel ridges which can then act as shear-cutting blades to break the food down.We use the Plains Zebra (Equus quagga) as a hypsodont, herbivorous model organism to investigate how initial wear of the tooth crown is controlled by underlying structures.We find that the enamel proportion is smaller at the apical half of the tooth crown in all upper tooth positions and suggest that lower enamel content here could promote early wear.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center of Natural History (CeNak), University of Hamburg , Hamburg , Germany.

ABSTRACT
Unworn teeth of herbivorous mammals are not immediately functional. They have to be partially worn to expose enamel ridges which can then act as shear-cutting blades to break the food down. We use the Plains Zebra (Equus quagga) as a hypsodont, herbivorous model organism to investigate how initial wear of the tooth crown is controlled by underlying structures. We find that the enamel proportion is smaller at the apical half of the tooth crown in all upper tooth positions and suggest that lower enamel content here could promote early wear. Besides this uneven enamel distribution, we note that the third molar has a higher overall enamel content than any other tooth position. The M3 is thus likely to have a slightly different functional trait in mastication, resisting highest bite forces along the tooth row and maintaining functionality when anterior teeth are already worn down.

No MeSH data available.


Related in: MedlinePlus